The development of addiction involves the dopaminergic reward pathway and downstream negative changes that lead to craving and repeat self-administration. While it is clear this process involves changes in neuronal plasticity t the synapse junction, the exact changes at the protein level leading to the development of dependence and negative responses associated with withdrawal are poorly understood, in large part because of the highly complex cellular and tissue organization and neuronal circuitry within the brain. To better understand this process requires proteomic approaches, which in turn require better detection reagents for the synapse proteome which comprises over 2,000 different proteins. We propose to use our proprietary yeast display antibody library to develop well-characterized, high-affinity, specific antibodies against a panel of synapse proteins, many of which have been shown to be modulated in response to opiate administration. In this Phase I/II study, antibodies against a panel of about 150 synaptic proteins will be developed and used to probe the changes of these proteins upon drug administration in a mouse model. The long-term goal is to develop novel and high quality detection reagents for the entire synapse proteome with our yeast display/antibody library system to better map the critical changes underlying addiction.